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picoCTF - Day 1 - Warm up

news 来源：原创 2024/5/20 12:42:10

Obedient Cat

Overview

Category: General Skills
Points: 5

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Solution

First download the file, it has no extension associated.
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Let’s see what kind of file it is using file command.

file flag

It’s ascii.
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cat to obtain flag.

cat flag

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flag: picoCTF{s4n1ty_v3r1f13d_28e8376d}

Mod 26

Overview

Category: Cryptography
Points: 10

Solution

Basic rot 13 cipher. Go to https://rot13.com/ to obtain flag.

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flag: picoCTF{next_time_I'll_try_2_rounds_of_rot13_TLcKBUdK}

Python Wrangling

Overview

Category: General Skills
Points: 10

Solution

First download all three files.

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After checking the python code, it looks like the script can decode the encoded flag using the password file.

Run the python script as there’s usage string.
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Pretty straight forward now.

# copy the password string
cat pw.txt

# run the script and paste in the password
python ende.py -d flag.txt.en

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flag: picoCTF{4p0110_1n_7h3_h0us3_dbd1bea4}

Wave a flag

Overview

Category: General Skills
Points: 10

Solution

First download the file.

It’s elf executable.
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Run it.

chmod +x warm
./warm

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Looks like the flag should be in the help info.

./warm -h

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flag: picoCTF{b1scu1ts_4nd_gr4vy_18788aaa}

information

Overview

Category: Forensics
Points: 10

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Solution

First download the file. It’s a jpg file. Must use one of the image meta data manipulation tools to check the file.

exiftool cat.jpg

This License file looks suspicious. Might be base64 encoded string.
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Decode it.

echo -n 'cGljb0NURnt0aGVfbTN0YWRhdGFfMXNfbW9kaWZpZWR9' | base64 -d

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flag: picoCTF{the_m3tadata_1s_modified}

Nice netcat…

Overview

Category: General Skills
Points: 15

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Solution

Connect to the server using the command and see.

nc mercury.picoctf.net 22902

Looks like ascii numbers. Do a string manipulation and convert them to letters.
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Concatenate into one line. Good that they have extra space for us.

nc mercury.picoctf.net 22902 | tr -d '\n' | tee flag.ascii

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Go to https://codebeautify.org/ascii-to-text to get the flag.

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flag: picoCTF{g00d_k1tty!_n1c3_k1tty!_d3dfd6df}

Summary

Day 1 out. Pretty straight forward and easy, hence warm up. Tomorrow we’re going to be facing harder ones involving reverse engineering problems. Game’s on.